Method of producing semiconductor device

ABSTRACT

A semiconductor device incorporating a capacitor structure that includes a ferroelectric thin film is obtained by forming, on a single crystalline substrate  10  having a surface suited for growing thereon a thin film layer of ferroelectric single crystal having a plane (111), a ferroelectric single crystalline thin film  12 ′ containing Pb and having a plane (111)  11  in parallel with the surface of the substrate (or a ferroelectric polycrystalline thin film containing Pb and oriented parallel with the plane (111) in parallel with the surface of the substrate) and part  16  of a circuit of a semiconductor device, to thereby fabricate the single crystalline substrate  10  having said ferroelectric thin film containing Pb and said part of the circuit of the semiconductor device; and bonding said single crystalline substrate  10  to another substrate on which the other circuit of the semiconductor device has been formed in advance, to couple the two circuits together. 
     The capacitor in the semiconductor device thus obtained includes a ferroelectric thin film having a large amount of polarizing charge. The semiconductor device can be used as a highly reliable nonvolatile memory.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims priority of Japanese PatentApplication No. 2002-328382 filed on Nov. 12, 2002, the contents thereofbeing incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a semiconductor device and,particularly, to a method of producing a semiconductor device having acapacitor structure which includes a ferroelectric thin film.

BACKGROUND ART

There are various known semiconductor devices, such as semiconductormemories. Among these memory devices, those that hold data even when thepower source is turned off are called nonvolatile memories. Among thenonvolatile memories, one using a ferroelectric material as a capacitormaterial for holding the electric charge is called ferroelectric memory(Ferroelectric Random Access Memory (FRAM, registered trademark)).

The FRAM utilizes two residual polarizing properties of dissimilarpolarities possessed by a ferroelectric thin film, and holds data evenwhen the power source is turned off. The possible number of times ofrewriting, which is an indication of nonvolatile property, is as greatas 1×10¹⁰ to 1×10¹² times. The rewriting speed is in the order ofseveral tens of nanoseconds, a very high speed.

In the FRAM, the ferroelectric material used for forming a capacitor canbe polarized in one of the two directions. By distinguishing thedirection of polarization, it is possible to store the data “1”corresponding to one direction of polarization and the data “0”corresponding to the opposite direction of polarization. When thedielectric material in the capacitor is not a ferroelectric material butis a paradielectric material, the polarization is maintained only whenthere is a potential difference from the electrodes but is notmaintained when the potential difference is removed. In this case,therefore, a volatile operation is brought about. The direction ofpolarization of the ferroelectric material in the FRAM can be detectedby applying a potential large enough for switching over the polarizationof the capacitor.

The ferroelectric materials used in the FRAM include a lead-basedferroelectric material and a bismuth-based ferroelectric material.Representative lead-based ferroelectric materials are PZT(PbZr_(x)Ti_(1-x)O₃), PLZT (Pb_(y)La_(1-y)Zr_(x)Ti_(1-x)O₃), etc. Arepresentative bismuth-based ferroelectric material is SBT (SrBi₂Ta₂O₉).

Concerning the ferroelectric material used in the FRAM, JapaneseUnexamined Patent Publication (Kokai) No. 13-102543 teaches the use of asingle crystalline ferroelectric thin film, as a ferroelectric material,for forming a capacitor in the FRAM. This publication, however, does notteach the method of producing semiconductor devices by using a singlecrystalline ferroelectric thin film grown on a single crystallinesubstrate, as in the present invention.

Japanese Unexamined Patent Publication (Kokai) No. 11-103024 teaches asemiconductor device of the structure in which a ferroelectric thin film(oriented polycrystalline thin film), having a plurality of crystallineparticles arranged as a layer, is formed on the lower electrode in whichcrystals constituting a surface that comes in contact with the thin filmare arranged on a plane (111).

Further, Foster et al., Journal of Applied Physics, 81, 2324, 1997,reports a thin PZT film having a large residual polarization charge(2Pr) obtained by forming (001) SrRuO₃ as a lower electrode on (001)SrTiO₃ and then forming a thin PZT (001) film by the MOCVD method.

A system LSI using a ferroelectric material for forming the capacitor asmentioned above must have very highly reliable, since it is used inequipment that deals with money data and data on individuals, such as ICcards, smart cards, etc. To realize a service life of ten years, asexpected for these system LSIs, it is desired that the polarizing chargeof the ferroelectric capacitor is as large as possible. With theferroelectric capacitors fabricated by the conventional sputteringmethod, however, the amount of polarizing charge was mostly from 20 to25 μC/cm², and it was difficult to obtain, maintaining a high yield,ferroelectric capacitors satisfying the amount of polarizing charge of30 μC/cm² that is necessary for practical products. It is even moredifficult to obtain a ferroelectric capacitor having the amount ofpolarizing charge of not smaller than 35 μC/cm² necessary for improvingthe reliability of the product.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a method which makesit possible to produce a highly reliable semiconductor deviceincorporating a capacitor structure that includes a ferroelectric thinfilm having a large amount of polarizing charge.

According to the method of producing a semiconductor device of thepresent invention, use is made of a single crystalline thin filmmaterial having a plane (111) or a polycrystalline thin film materialoriented parallel to a plane (111) as a ferroelectric crystallinematerial, and electrodes are formed on both surfaces thereof, to producesemiconductor devices including a capacitor having a residual polarizingamount greater than that of the conventional capacitors using theoriented polycrystalline thin film.

Specifically, the present invention is concerned with a method ofproducing a semiconductor device incorporating a capacitor structurethat includes a ferroelectric thin film, characterized by:

forming, on a single crystalline substrate having a surface suited forgrowing thereon a thin film layer of ferroelectric single crystal havinga plane (111), a ferroelectric single crystalline thin film containingPb and having a plane (111) in parallel with the surface of thesubstrate or a ferroelectric polycrystalline thin film containing Pb andoriented parallel with the plane (111) in parallel with the surface ofthe substrate, and part of a circuit of a semiconductor device, tothereby fabricate a single crystalline substrate having saidferroelectric thin film containing Pb and said part of the circuit ofthe semiconductor device; and

bonding said single crystalline substrate to another substrate on whichthe other circuit of the semiconductor device has been formed inadvance, to couple the two circuits together to thereby obtain asemiconductor device incorporating a capacitor structure that includes aferroelectric thin film.

According to one embodiment of the present invention, there is provideda method of producing a semiconductor device incorporating a capacitorstructure that includes a ferroelectric thin film, comprising:

(1) forming, on a single crystalline substrate, a ferroelectric singlecrystalline thin film layer containing Pb and having a plane (111) inparallel with the surface of the substrate, patterning said thin filmlayer to thereby form isolated ferroelectric thin films of apredetermined shape on the single crystalline substrate, forming oneelectrode of a capacitor of a predetermined shape positioned on saidferroelectric thin film, and forming part of a circuit of asemiconductor device on the single crystalline substrate, to therebyfabricate a single crystalline substrate having thereon saidferroelectric thin film containing Pb, said one electrode and said partof the circuit of the semiconductor device;(2) fabricating a semiconductor substrate having the other circuit ofthe semiconductor device formed;(3) bonding said single crystalline substrate to said semiconductorsubstrate to couple the circuits of the two substrates together; and(4) removing said single crystalline substrate to expose theferroelectric thin film, and forming another electrode of the capacitoron the ferroelectric thin film that is exposed.

According to another embodiment of the present invention, there isprovided a method of producing a semiconductor device incorporating acapacitor structure that includes a ferroelectric thin film, comprising:

(1) forming an electrically conducting thin film layer on a singlecrystalline substrate having through holes, forming, on saidelectrically conducting thin film layer, ferroelectric singlecrystalline thin film layer containing Pb and having a plane (111) inparallel with the surface of the substrate, or a ferroelectricpolycrystalline thin film layer containing Pb and oriented parallel withthe plane (111) in parallel with the surface of the substrate,patterning said electrically conducting thin film layer and saidferroelectric thin film layer to thereby form isolated ferroelectricthin films of a predetermined shape and one electrode of a capacitor ofa predetermined shape, forming another electrode of the capacitor onsaid ferroelectric thin film, and forming part of a circuit of asemiconductor device so as to pass through the holes in said singlecrystalline substrate, to thereby fabricate a single crystallinesubstrate comprising a capacitor structure constituted by saidferroelectric thin film containing Pb and a pair of electrodes holdingthe ferroelectric thin film therebetween, and said part of the circuitof the semiconductor device;(2) fabricating a semiconductor substrate having the other circuit ofthe semiconductor device formed; and(3) bonding said single crystalline substrate to said semiconductorsubstrate to couple the circuits of the two substrates together.

In the method of the present invention, a dielectric thin film of thecapacitor is formed from a ferroelectric material containing lead (Pb).As the ferroelectric material containing Pb, there can be used PZT(PbZr_(x)Ti_(1-x)O₃), PLZT (Pb_(y)La_(1-y)Zr_(x)Ti_(1-x)O₃), PLCSZT((Pb, La, Ca, Sr)(Zr, Ti)O₃) or a substance derived therefrom by addingNb thereto.

As the single crystalline substrate for forming the ferroelectric thinfilm thereon, there can be used a single crystalline substrate having aplane (111) on which the ferroelectric thin film is formed, or a singlecrystalline substrate having an offset angle from the plane (111). Ingeneral, use of the single crystalline substrate having an offset angleincreases the flatness of the surface of the grown crystals. As atypical example of the single crystalline substrate having the plane(111), there can be exemplified an MgO or SrTiO₃ single crystallinesubstrate.

Alternatively, as the single crystalline substrate for forming theferroelectric thin film thereon, there may be used an α-Al₂O₃ singlecrystalline substrate having a plane (0001) (C-plane) on which theferroelectric thin film is to be formed, or an α-Al₂O₃ singlecrystalline substrate having an offset angle from the plane (0001).There may be also used an MgAl₂O₄ (magnesia spinel) single crystallinesubstrate having a plane (001) on which the ferroelectric thin film isto be formed.

When the above-mentioned substrate (MgO, SriO₃, α-Al₂O₃ or MgAl₂O₄single crystalline substrate) for forming the ferroelectric thin film isto be used, there may be formed an electrically conducting thin film,that serves as one electrode of the capacitor, on the substrate prior toforming the ferroelectric polycrystalline thin film layer. Theelectrically conducting thin film can be formed from Pt, Ir, Ti, Ru oran oxide thereof, and the plane (111) thereof can be used as the surfaceon which the ferroelectric thin film is formed.

Alternatively, as the single crystalline substrate for forming theferroelectric thin film thereon, there can be used a single crystallinesilicon substrate having a plane (111) on which the ferroelectric thinfilm is to be formed, or having a plane equivalent thereto, i.e., havinga plane {111}, or a single crystalline silicon substrate having anoffset angle from the plane {111}. Also, there may be used a singlecrystalline silicon substrate having a plane {100} on which theferroelectric thin film is to be formed, or a single crystalline siliconsubstrate having an offset angle from the plane {100}.

When such a single crystalline silicon substrate is used, theferroelectric thin film can be epitaxially grown on the ferroelectricthin film-forming surface of the substrate directly, or through a bufferlayer formed thereon. Use of the buffer layer is effective in preventingthe formation of silicide during the formation of the ferroelectric thinfilm. The buffer layer may be formed of MgO, YSZ (yttrium-stabilizedzirconia (ZrO₂)), MgAl₂O₄, CaO, SrTiO₃, CeO₂ or the like, the plane(111) or the plane (0001) of which can be used for the formation of theferroelectric thin film.

When the single crystalline silicon substrate is used and theferroelectric thin film is formed on the ferroelectric thin film-formingsurface of the substrate directly or through the buffer layer, anelectrically conducting thin film that serves as one electrode of thecapacitor may be formed on the substrate or on the buffer layer prior toforming the ferroelectric polycrystalline thin-film layer. Theelectrically conducting thin film can be formed of Pt, Ir, Ti, Ru or anoxide thereof, and the plane (111) thereof can be used as the surface onwhich the ferroelectric thin film is formed. Also, an alloy of thesemetal elements can be used. Further, a plurality of layers of the abovemetals or of the alloys thereof may be stacked. Alternatively, theelectrically conducting thin film may be formed of SrRuO₃, YBCO or LSCO,and the plane (111) thereof may be used as the surface for forming theferroelectric thin film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1E illustrate the steps in the former half of the method ofproducing semiconductor devices of Example 1;

FIGS. 2A to 2C illustrate the steps in the latter half of the method ofproducing semiconductor devices of Example 1;

FIGS. 3A to 3F illustrate the fabrication of a single crystallinesubstrate having a capacitor used in the production of the semiconductordevices of Example 2 formed;

FIG. 4 illustrates a semiconductor device produced by turning the singlecrystalline substrate having the capacitor of Example 2 formed upsidedown and bonding it to a silicon substrate having a semiconductorcircuit formed;

FIG. 5 illustrates a semiconductor device produced without turning thesingle crystalline substrate having the capacitor of Example 2 formedupside down but bonding it to the silicon substrate having thesemiconductor circuit formed; and

FIGS. 6A to 6F illustrate the fabrication of a single crystallinesubstrate having a capacitor to be used for the production ofsemiconductor devices of Example 3 formed.

BEST MODE FOR CARRYING OUT THE INVENTION

In the present invention, there is formed, on a singe crystallinesubstrate, a ferroelectric single crystalline thin film layer having aplane (111) in parallel with the surface of the substrate and containingPb. Foster et al., Journal of Applied Physics, 81, 2324, 1997 reportsthat when (001) SrRuO₃ was formed as a lower electrode on (001) SrTiO₃and a PZT thin film having a plane (001) was then formed by anorganometal chemical vapor phase deposition (MOCVD) method, the thinfilm had a residual polarization charge amount (2Pr) of as large as 110μC/cm². This shows that if calculated on the plane (111), the amount ofresidual polarization charge becomes 63 μC/cm² which is more than twiceas great as 30 μC/cm² needed for the practical products as describedabove.

When, for example, a PZT material is used as the ferroelectric material,the axis of polarization exists in the (001)-direction when the type ofcrystals is cubic. When the plane (111) of the ferroelectric thin filmsingle crystal is formed on the electrode, the axis <111> perpendicularto the surface of the electrode has an angle of 35.3° with respect tothe axis of polarization <001>. The polycrystalline ferroelectric thinfilm has a domain structure of 30 to 100 nm, and exhibits only a smallamount of polarization charge as compared to that of the singlecrystalline thin film due to fluctuation in the azimuth of the axis ofpolarization.

Therefore, by forming, on the single crystalline structure, aferroelectric single crystalline thin film layer having a plane (111) inparallel with the surface of the substrate, etching the thin film layerto thereby form isolated ferroelectric thin films of a predeterminedshape on the single crystalline substrate, forming electrodes on bothsurfaces of the thin film, and bonding the single crystalline substrateto another substrate on which a semiconductor circuit has been formed tocouple the two circuits together, there can be produced a highlyreliable semiconductor device incorporating a capacitor which includes asingle crystalline ferroelectric thin film exhibiting the amount ofpolarizing charge which is no smaller than twice as large as the amountof polarizing charge, 30 μC/cm², of the conventional orientedpolycrystalline thin films.

The semiconductor device produced according to the present invention hasa large amount of polarization charge per a unit area of theferroelectric thin film used for the capacitor and, accordingly, makesit possible to secure a required amount of polarizing charge even if thecapacitor area is decreased. This makes it possible to carry outmicrofabrication according to the rule of scaling and, hence, to producea semiconductor device having a high degree of integration at adecreased cost while maintaining high performance.

EXAMPLES

The invention will now be further described by way of examples to which,however, the invention is in no way limited.

Example 1

As shown in FIG. 1A, a single crystalline PZT layer 12 is epitaxiallygrown on a single crystalline substrate 10, the single crystalline PZTlayer 12 having a plane (111) 11 in parallel with the surface of thesubstrate 10. As the single crystalline substrate 10, there can be useda substrate having, for example, a MgO plane (111), an SrTiO₃ plane(111) or an α-Al₂O₃ plane (0001).

The single crystalline PZT (111) can be epitaxially grown by anorganometal chemical vapor phase deposition (MOCVD) method, a molecularbeam epitaxy (MBE) method or a pulse laser deposition (PLD) method. Thefilm-forming methods are not limited thereto. Also, by not being limitedto PZT (PbZr_(x)Ti_(1-x)O₃), there can be used such ferroelectricmaterial as PLZT (Pb_(y)La_(1-y)Zr_(x)T_(1-x)O₃), PLCSZT ((Pb, La, Ca,Sr)(Zr, Ti)O₃), as well as a material derived therefrom by adding Nbthereto.

For example, the formation of PZT film by the MOCVD method can becarried out by using Pb(THD)₂, Zr(THD)₄ and Ti(i-PrO)₂(THD)₂ as startingmaterials at a substrate temperature of 550 to 600° C. and a pressure of130 to 670 Pa (1 to 5 Torr). In the formulas of these startingcompounds, THD stands for a trimethylhexane dionate, and i-PrO standsfor an isopropoxy.

The thin film layer 12 having the flat PZT plane (111) 11 is formed onthe whole surface of the substrate 10 and is, then, etched leaving thethin film 12′ in a region in which a thin-film capacitor is to be made(FIG. 1B). On the PZT thin film 12′, that is left, is formed a lowerelectrode 14 (which will be turned upside down when it is to be bondedto another substrate at a subsequent step) by a thin film of Pt or Irmaterial. On the substrate 10 is formed a plug 16 of tungsten (FIG. 1C)which will be a part of the circuit of a semiconductor device and is aninterconnection connected to another substrate (semiconductor substrate)to which the substrate is to be bonded later.

Next, a layer of an insulating material such as TEOS is formed on thesubstrate 10, and the surface thereof is planarized by a planarizationmethod such as CMP to form an insulating film 18 (FIG. 1D). Thereafter,thin tungsten films 20 are formed on the lower electrode 14 and on thetungsten plug 16, and the TEOS insulating layer is formed again and isthen planarized to thereby form an interlayer insulating film 22 (FIG.1E).

As shown in FIG. 2A, the substrate 10 on which the ferroelectric PZTthin film 12′ for capacitor is formed, is turned upside down so as toface a semiconductor substrate 24 on which there has been formed, inadvance, a transistor 23 as part of the circuit of the semiconductordevice. Subsequently, as shown in FIG. 2B, the substrate 10 isintimately adhered to the substrate 24 so that the thin tungsten film 20of the substrate 10 is joined to the interconnecting electrode 26 of thetransistor of the substrate 22, followed by the heat treatment to bondthe two substrates together and to mechanically and electrically couplethem together. Techniques for bonding two pieces of substrates in theform of wafers by the heat treatment have been disclosed in, forexample, Japanese Unexamined Patent Publications (Kokai) Nos. 2-303114and 1-115143.

Next, the substrate 10 used for forming the ferroelectric PZT thin film12′ for the capacitor is removed. The substrate 10 is removed bychemical dissolution using HCl when the substrate 10 is an MgOsubstrate. In the case of an SrTiO₃ substrate, it is chemicallydissolved using a mixed acid of HNO₃, HF and HCl. A sapphire (α-Al₂O₃)substrate can be dissolved only with molten KOH and, therefore, it ismechanically removed using an SiC abrasive or is. mechanically andchemically removed using colloidal silica.

Finally, as shown in FIG. 2C, there are formed an upper electrode 28 ofthe capacitor, a thin tungsten film 30 connected thereto, anothertungsten plug 32 connecting to the tungsten plug 16, and an interlayerinsulating film 34 in the same manner as described above, to therebyprovide a semiconductor device having a ferroelectric capacitor 36constituted of the lower electrode 14, ferroelectric PZT thin film 12′and upper electrode 28. The upper electrode 28 can be formed using, forexample, Ir or IrO₂.

Example 2

This example illustrates the production of a semiconductor deviceincorporating a ferroelectric capacitor by forming a PZT thin film onthe plane (0001) of a sapphire (α-Al₂O₃) substrate having through holesformed.

As shown in FIG. 3A, through holes 52 a, 52 b are perforated in asapphire (α-Al₂O₃) single crystalline substrate 50 having a plane (0001)51 as the upper surface. The through hole 52 a is for forming a plugthat will connect to one electrode of the capacitor and the through hole52 b is for forming a plug that will serve as an interconnection to beconnected to a semiconductor substrate (circuit board) that is to bebonded later. These through holes may be perforated by machining thesapphire substrate 50, or by a dry etching method using a reactive gasor an ionic milling method using Ar ions, or by chemical etching usingmolten KOH.

As shown in FIG. 3B, a thin film 54 is formed on the plane (0001) 51 ofthe substrate 50, the thin film 54 having a plane (111) 55 in parallelwith the plane 51. The thin film 54 will form one electrode of theferroelectric capacitor, and can be formed of Pt or Ir. On the thin film54 is further formed a PZT thin film 56 having a plane (111) 57 inparallel with the plane (0001) 51 of the substrate 50. The PZT thin filmgrown on the Pt plane (111) or on the Ir plane (111) has a latticeconstant that does not correspond with that of the Pt or Ir crystal, andis therefore not formed as a complete single crystal but as apolycrystalline thin film (polycrystalline thin film oriented paralletwith the plane (111)) which is strongly oriented. A single crystallinePZT thin film can be obtained if there is used an SrRuO₃ thin filminstead of the Pt or Ir thin film. Next, as shown in FIG. 3C, thin films56 and 54 (FIG. 3B) are removed but leaving a portion that will forms aferroelectric thin film 58 of the capacitor and a portion that forms anelectrode 60.

As shown in FIG. 3D, the through holes 52 a and 52 b (FIG. 3C) arefilled with tungsten, and a plug 62 a of tungsten extending from thetungsten in the through hole 52 a is formed to be connected to theelectrode 60. Tungsten material in a columnar form is extended from thetop of the tungsten in the through hole 52 b, to form a plug 62 b thatwill form an interconnection to be connected to the semiconductorsubstrate that is bonded subsequently.

A layer of an insulating material such as TEOS is formed on thesubstrate 50, and the surface thereof is planarized to form aninsulating film 64 (FIG. 3E). Next, as shown in FIG. 3F, anotherelectrode 66 of a Pt or Ir thin film is formed on the ferroelectric thinfilm 58, the electrode 66 having a plane (111) in parallel with thesurface of the substrate 50. Thin tungsten films 68 a and 68 b areformed on the electrode 66 and on the tungsten plug 62 b, respectively.A TEOS insulating layer is formed again and is then planarized to forman interlayer insulating film 70 (FIG. 3F).

In this example, the substrate 50 having the capacitor formed, thecapacitor being constituted by the ferroelectric thin film 58 and thetwo electrodes 60 and 66 holding it therebetween, can be turned upsidedown, and can be bonded to the another substrate in which the transistorhas been formed in advance, or can be bonded thereto without beingturned upside down. When the substrate 50 is turned upside down as shownin FIG. 4, the electrode 66 of the capacitor forms the lower electrodeand is connected, through the thin tungsten film 68 a, to oneinterconnecting electrode 78 a of the transistor 76 formed in theanother substrate (semiconductor substrate) 74, and the tungsten plug 62b is connected to the another interconnecting electrode 78 b through thethin tungsten film 68 b. When the substrate 50 is not turned upside downas shown in FIG. 5, the electrode 60 of the capacitor forms the lowerelectrode and is connected, through the tungsten plug 62 a, to oneinterconnecting electrode 78 a of the transistor 76 of the anothersubstrate 74, and the tungsten plug 62 b is connected to the anotherinterconnecting electrode 78 b.

Example 3

This example illustrates the production of a semiconductor deviceincorporating a ferroelectric capacitor by forming a PZT thin film onthe plane (111) of the silicon substrate having through holes formed.

As shown in FIG. 6A, through holes 92 a, 92 b are perforated in asilicon substrate 90 having a plane (111) 91 as an upper surface. Thethrough hole 92 a is for forming a plug that will connect to oneelectrode of the capacitor and the through hole 92 b is for forming aplug that will serve as an interconnection to be connected to asemiconductor substrate that is to be bonded later. These through holesmay be perforated by machining the silicon substrate 90, or by a dryetching method using a reactive gas or an ionic milling method using Arions, or by chemical etching using a mixed acid of HF and HNO₃.

As shown in FIG. 6B, a thin MgAl₂O₄ film 94 is formed on the plane (111)91 of the substrate 90, the thin film 94 having a plane (111) 95 inparallel with the plane 91. The thin film 94 serves as a buffer layerfor forming thereon a PZT thin film having a plane (111) in parallelwith the plane (111) 91 of the substrate 90, and has the function ofpreventing the formation of silicide during the formation of the PZTthin film. Then, a thin film 96 that will serve as one electrode of theferroelectric capacitor is formed of Pt or Ir on the thin film 94. Thethin film 96, too, has a plane (111) 97 in parallel with the plane (111)91 of the substrate 90. On the thin film 96 is further formed a PZT thinfilm 98 having a plane (111) 99 in parallel with the plane (111) 91 ofthe substrate 90.

Next, as shown in FIG. 6C, thin films 98 and 96 (FIG. 6B) are removedbut leave a portion that forms a ferroelectric thin film 100 of thecapacitor and a portion that forms an electrode 102.

Subsequently, as shown in FIG. 6D, the through holes 92 a and 92 b (FIG.6C) are filled with tungsten, and a plug 104 a of tungsten extendingfrom the tungsten in the through hole 92 a is formed to be connected tothe electrode 102. Tungsten material in a columnar form is extended fromthe top of the tungsten in the through hole 92 b to form a plug 104 bthat will form an interconnection to be connected to the semiconductorsubstrate that is bonded subsequently.

A layer of an insulating material such as TEOS is formed on thesubstrate 90, and the surface thereof is planarized to form aninsulating film 106 (FIG. 6E). Next, as shown in FIG. 6F, anotherelectrode 108 of a Pt or Ir thin film is formed on the ferroelectricthin film 100, the electrode 108 having a plane (111) in parallel withthe surface of the substrate 90. Thin tungsten films 110 a and 110 b areformed on the electrode 108 and on the tungsten plug 104 b,respectively. A TEOS insulating layer is formed again and is thenplanarized to form an interlayer insulating film 112 (FIG. 6F).

In this example, too, as described in example 2, the substrate 90 havingthe capacitor formed, the capacitor being constituted by theferroelectric thin film 100 and the two electrodes 102 and 108 holdingit therebetween, can be turned upside down and be bonded to the anothersubstrate in which the transistor has been formed in advance, or can bebonded thereto without being turned upside down.

Example 4

This Example illustrates the production of a semiconductor deviceincorporating a ferroelectric capacitor by forming a PZT thin film onthe plane (001) of the silicon substrate having through holes formed,the PZT thin film having a plane (111) in parallel with the plane (001).

In the same manner as described in the example 3, in the siliconsubstrate having the plane (001) as an upper surface are perforated athrough hole for forming a plug that will connect to one electrode ofthe capacitor and a through hole for forming a plug that will serve asan interconnection to be connected to a semiconductor substrate that isto be bonded subsequently.

In general, a thin oxide film (native oxide) exists on the surface of asilicon substrate. Here, a thin MgAl₂O₄ film is formed on the plane(001) of the silicon substrate on which the oxide film is left. The thinMgAl₂O₄ film formed on the Si plane (001) where the thin oxide film ispresent, is a film possessing a plane (111), which forms a buffer layerfor forming thereon a PZT thin film that has a plane (111) in parallelwith the surface (thin film-forming surface) of the silicon substrate asdescribed in example 3, and can prevent the formation of silicide duringthe formation of the PZT thin film.

Subsequently, a capacitor is formed on the silicon substrate accordingto the procedure earlier described in example 3. The substrate is bondedto another substrate in which the transistor has been formed in advance,to thereby produce a semiconductor device incorporating theferroelectric PZT capacitor.

INDUSTRIAL APPLICABILITY

The semiconductor device of the invention uses a single crystal having asurface of plane (111) which is perpendicular to the axis <111> havingan angle of 35.3° with respect to the axis of polarization, as aferroelectric thin film for a capacitor. The single crystallineferroelectric thin film has an amount of polarizing charge that iscalculated to be 63 μC/cm², which is not smaller than two times as much,30 μC/cm², as that of the conventional oriented polycrystalline thinfilm. Owing to its large amount of residual polarization, a very highdegree of reliability is exhibited by a system LSI that incorporates, asnonvolatile memories, the semiconductor devices that are obtained byutilizing the present invention.

Besides, the semiconductor device obtained by the present invention hasa large amount of polarizing charge per a unit area, making it possibleto secure a required amount of polarization charge even when thecapacitor area is decreased. This makes it possible to carry outmicrofabrication according to the rule of scaling and, hence, to producea semiconductor device having a high degree of integration at adecreased cost while maintaining high performance.

1. A method of producing a semiconductor device comprising: (1)epitaxially forming an electrically conducting thin film layer on asingle crystalline substrate having through holes, epitaxially forming,on said electrically conducting thin film layer, ferroelectric singlecrystalline thin film containing Pb and having a plane (111) in parallelwith the surface of the substrate, patterning said electricallyconducting thin film layer and said ferroelectric thin film layer tothereby form isolated ferroelectric thin films of a predetermined shapeand one electrode of a capacitor of a predetermined shape, forminganother electrode of the capacitor on said ferroelectric thin film, andforming part of a circuit of a semiconductor device so as to passthrough the holes in said single crystalline substrate, to therebyfabricate a single crystalline substrate comprising a capacitorstructure constituted by said ferroelectric thin film containing Pb anda pair of electrodes holding the ferroelectric thin film therebetween,and said part of the circuit of the semiconductor device; (2)fabricating a semiconductor substrate having another circuit of thesemiconductor device formed; and (3) bonding said single crystallinesubstrate to said semiconductor substrate to couple the circuits of thetwo substrates together.
 2. A method of producing a semiconductor deviceaccording to claim 1, wherein said ferroelectric material is PZT(PbZr_(x)Ti_(1-x)O₃), PLZT (Pb_(y)La_(1-y)Zr_(x)Ti_(1-x)O₃), PLCSZT((Pb, La, Ca, Sr)(Zr, Ti)O₃) or a substance derived therefrom by addingNb thereto.
 3. A method of producing a semiconductor device according toclaim 1, wherein as said single crystalline substrate, a singlecrystalline substrate having a plane (111) on which the ferroelectricthin film is to be formed, or a single crystalline substrate having anoffset angle from the plane (111) is used.
 4. A method of producing asemiconductor device according to claim 3, wherein said singlecrystalline substrate is an MgO or SrTiO₃ single crystalline substrate.5. A method of producing a semiconductor device according to claim 1,wherein as said single crystalline substrate, an α-Al₂O₃ singlecrystalline substrate having a plane (0001) on which the ferroelectricthin film is to be formed, or an α-Al₂O₃ single crystalline substratehaving an offset angle from the plane (0001), is used.
 6. A method ofproducing a semiconductor device according to claim 1, wherein as saidsingle crystalline substrate an MgAl₂O₄ single crystalline substratehaving a plane (001) on which the ferroelectric thin film is to beformed, is used.
 7. A method of producing a semiconductor deviceaccording to claim 1, wherein as said single crystalline substrate asingle crystalline silicon substrate having a plane {111} on which theferroelectric thin film is to be formed or a single crystalline siliconsubstrate having an offset angle from the plane {111}, is used.
 8. Amethod of producing a semiconductor device according to claim 7, whereinsaid ferroelectric thin film is epitaxially grown directly on theferroelectric thin film-forming surface of said single crystallinesubstrate.
 9. A method of producing a semiconductor device according toclaim 7, wherein said ferroelectric thin film is epitaxially grownthrough a buffer layer formed on the ferroelectric thin film-formingsurface of said single crystalline substrate.
 10. A method of producinga semiconductor device according to claim 9, wherein said buffer layeris formed of MgO, yttrium-stabilized zirconia, MgAl₂O₄, CaO, SrTiO₃ orCeO₂, and said ferroelectric thin film is grown on the plane (111) orthe plane (0001) thereof.
 11. A method of producing a semiconductordevice according to claim 1, wherein as said single crystallinesubstrate, a single crystalline silicon substrate having a plane {100}on which the ferroelectric thin film is to be formed, or a singlecrystalline silicon substrate having an offset angle from the plane{100}, is used.